Ferroelectric layers are employed in components, use being made of the dielectric, pyroelectric and piezoelectric properties of ferroelectrics. Examples of components having ferroelectric layers include capacitors, pyrodetectors, piezoactuators or semiconductor memories, it being possible in the latter case for the ferroelectric layers to be used both as a dielectric and as a storage medium by exploiting the hysteresis effect in relation to polarization.
European reference EP 0 698 918 A discloses a microelectronic layer structure which consists of an oxidizable substrate, an electrode and a dielectric having high dielectric constant. An isolating layer is arranged between the electrode and the substrate. The isolating layer, which for example consists of a noble-metal/insulator alloy and must be electrically conductive, has the primary purpose of limiting diffusion of oxygen to the surface of the substrate.
Great importance has been placed on components having thin films of ferroelectrics, which can be produced with a high degree of structural quality. To this end, it is customary to produce a first electrode layer on a substrate, and the ferroelectric layer on top using conventional thin-film processes. Platinum is particularly suitable as the electrode material for the electrode lying below the ferroelectric layer, since this material can withstand the deposition conditions for the ferroelectric layer, at high temperatures and in an oxygen-containing atmosphere, without sustaining damage and does not cause any diffusion into the ferroelectric layer, which might cause a change in composition and therefore a change in properties.
When silicon-containing substrates are used, the problem arises that platinum exhibits only moderate adhesion to silicon oxide. For the production of storage capacitors having platinum electrodes, titanium adhesion layers have therefore already been proposed, which are arranged between the platinum electrode and the substrate surface containing silicon oxide (see, for example, H. N. Al-Shareef et al., Proc. 4th International Symposium on Integrated Ferroelectrics, Mar. 9-11, 1992, pages 181-196, Montery, Calif., USA).
However, titanium-containing adhesion layers entail a number of disadvantages, leading to degradation of the electrical properties of ferroelectric capacitors and, in general, of ferroelectric components. Good ferroelectric properties are obtained only with ferroelectrics which contain crystalline oxides and are produced at elevated temperature in oxygen-containing atmospheres. In this case, however, diffusion of titanium into the platinum and subsequent oxidation of the titanium to form titanium oxide TiO.sub.2 are observed. This entails a quite significant increase in volume, which causes the formation of so-called hillocks on the surface of the platinum electrode. These structural irregularities continue in a ferroelectric layer applied on top, cause an unfavorable morphology in it and therefore lead to unfavorable electric and ferroelectric properties. In the extreme case, the structural irregularity of the platinum electrode is so great as to bring about a short-circuit in the ferroelectric component, and therefore complete failure of the component.